This invention relates to a novel process for preparing 1,5-benzothiazepine derivatives of the formula: ##STR3## wherein R.sup.1 is a lower alkyl group, or a salt thereof.
The above 2-(4-lower alkoxyphenyl)-3-hydroxy-2,3-dihydro-1,5-benzothiazepin-4(5H)-one is useful as an intermediate for the synthesis of medical compounds, for the example, (+)-cis-2-(4-methoxyphenyl)-3-acetoxy-5-(.beta.-dimethylaminoethy l)-2,3-dihydro-1,5-benzothiazepin-4(5H)-one (generic name: Diltiazem) which is excellent coronary vasodilator.
Heretofore, there have been known that said intermediate can be prepared by the two steps of, for example, hydrolyzing ethyl 2-hydroxy-3-(2-aminophenylthio)-3-(4-methoxyphenyl)propionate with alkali to give corresponding free acid and then subjecting it to intramolecular cyclization under heating (Japanese Patent Publication (examined) No. 8982/1971).
It is an object of the present invention to provide a novel process for preparing said intermediates from 2-hydroxy-3-(2-aminophenylthio)-3-(4-lower alkoxyphenyl)propionate in a high yield by one step.